Non linear optical material and method for orientation thereof

ABSTRACT

A nonlinear optical material comprises a solid solution of an organic guest compound having an electron donative group or an electron attractive group. The organic guest compound is contained in the nonlinear optical material preferably an oriented form through orientation under melting by application of a DC electric field. The guest compound is preferably a para-di-substituted benzene derivative represented by the formula: ##STR1## wherein A is an electron donative group and B is an electron attractive group.

This application is a continuation of application Ser. No. 07/697,007filed May 8, 1991, now abandoned, which is a continuation of applicationSer. No. 07/629,165 filed Dec. 19, 1990, issued as U.S. Pat. No.5,037,582 on Aug. 6, 1991, which is a continuation of application Ser.No. 07/164,414 filed Mar. 4, 1988, now abandoned.

FIELD OF THE INVENTION AND RELATED ART

The present invention relates to a nonlinear optical material, moreparticularly to a nonlinear optical material suitable for a waveguide inthe form of a film or fiber, and a method for orientation thereof.

Heretofore, as nonlinear optical materials, inorganic single crystals ofKDP, LiNbO₃, etc., and organic single crystals of urea, etc., have beenknown and used, e.g., for a wavelength conversion element for laser.However, it is technically difficult to obtain such a single crystal ina large size, and such a single crystal cannot be obtained at a lowcost. In view of these problems, it has been tried to obtain a largesize of single crystal in the form of a film or fiber through vapordeposition or zone melting in a capillary (Nayay, B. K.; ACS sym., 153(1983)). By this method, however, it is not easy to control the growthof single crystal in a direction capable of phase matching required foreffectively providing second harmonic generation (abbreviated as "SHG")or third harmonic generation (abbreviated as "THG").

Instead of using a single crystal, there has been known a method ofadding a guest compound having a large nonlinear optical constant inhost molecules and applying an electric or magnetic field fororientation of the mixture in order to control the crystallinestructure.

For example, it was tried to use a polymer liquid crystal as a host andpolar molecules as a guest and utilize the orienation under electricfield of the polymer liquid crystal to align the polar molecules. As aresult, SHG was observed under application of an electric field(Meredity, G. R., et al.; Macromolecules, 15, 1385 (1982)).

Further, as an example of alignment of polar molecules in an amorphouspolymer, a polymethyl methacrylate resin with an azo colorant dissolvedtherein was formed into a film, heated to a temperature above the glasstransition point and supplied with a voltage to align the azo colorantmolecules, followed further by cooling to fix the resultant structure.As a result, a nonlinear optical constant of 6×10⁻⁹ esu was observed(Singer, K. D., Sohn, J. E. and Lalama, S. J.; Appl. Phys, Lett. 49,page 248 (1986)).

It has been also proposed to mix a nonlinear optical-responsive organiccompound in a polymer to obtain a polymer nonlinear optical material(U.S. Pat. No. 4,428,873; JP-A (Kokai) 57-45519). A nonlinear opticalmaterial comprising an acrylamide resin as a host polymer and anonlinear optical-responsive organic compound as a guest has been alsoproposed (JP-A (Kokai) 62-84139). It has been also proposed to causecrystalline growth of a compound having an asymmetric center in apolyoxyalkylene matrix (JP-A 62-246962).

Such a polymer-type nonlinear optical material has an excellentprocessibility into a film, etc., while retaining its electroninteraction providing a nonlinear optical effect and is regarded as asuitable material for device formation.

Such a polymer-type nonlinear optical material, however, still involvessome problems. Generally, a larger nonlinear optical effect is attainedproportionally as the content of a guest compound in a polymer matrix(solid solution) is increased. It is however difficult to blend alow-molecular weight polar compound as a guest in a large proportion,e.g., at least 20 wt. %, in a polymer uniformly on a molecular level, sothat the guest molecules can partially cause phase separation to becrystallied.

Furthermore, such a polymer blend is liable to lose the flexibility ofthe polymer per se and result in a remarkable decrease in mechanicalstrength, especially where the content of a low-molecular weight polarguest compound is increased.

Further, as for the second order nonlinear optical effect, a guestmolecule which per se has a large polarization β can show no or only aslight SHG activity when blended in a conventional polymer, if it is acentrosymmetric crystal. For this reason, it has been generallynecessary to form the polymer blend into a film and orient the film asby application of an electric or magnetic field or by stretching.

Particularly, in the systems proposed heretofore, a good molecularorientation or a large nonlinear susceptibility could not be obtainedbecause the electric field energy is smaller than the thermal energy asdescribed in the above-mentioned report by Singer, K. D. Further, nopolymer optical modulation material obtained by addition of a nonlinearoptical-responsive organic compound could show a nonlinearsusceptibility exceeding that of the nonlinear optical-responsiveorganic compound alone.

In order to obtain a large nonlinear optical effect for a nonlinearelement, it has been considered to increase the energy density ofincident light. For this purpose, it is necessary to use a high energylaser beam or to focus the incident light. Particularly, the focusing isimportant when a semiconductor laser beam is applied to a nonlinearoptical element. Especially suitable for this purpose is focusing ofincident light by use of a waveguide in the form of a film or fiber. Alarge nonlinear optical effect as a result has been reported (T.Taniguchi, JEE. High Tech. Report, November, 93 (1986)). In order toobtain such a waveguide, however, diffusion-exchange of Ti or H in asingle crystal was effected, for example, for LiNbO₃. It took much timeand the control was difficult.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a nonlinear opticalmaterial which substitutes for a conventional expensive nonlinearoptical material of a single crystal, has a sufficient nonlinear opticalconstant and is applicable for a waveguide.

A more specific object of the present invention is to provide a novelnonlinear optical material, wherein a nonlinear guest organic compoundhaving a large polarization is easily and uniformly dissolved mutuallyin a host polymer compound; the second order and third order nonlinearoptical effects of the guest organic compound are not lowered byblending with the host polymer compound; a flexibility is retained evenif the guest organic compound is contained in a large proportion; andexcellent mechanical strength and processability are retained.

Another object of the present invention is to provide a nonlinearoptical material wherein a guest organic compound having a largepolarization β but showing no SHG activity because of its crystallinecentrosymmetry is blended within a host polymer compound to develop alarge SHG activity.

Still another object of the present invention is to provide an effectiveorientation method for such a nonlinear optical material.

According to the present invention, there is provided a nonlinearoptical material which comprises a solid solution of an organic guestcompound having at least one of an electron donative group and anelectron attractive group.

It has been also found more effective to use, as the guest compound, acompound of a para-di-substituted benzene structure having the electrondonative group and the electron attractive group at the para positions.Based on the above knowledge, according to a specific aspect of thepresent invention, there is also provided a nonlinear optical materialwhich comprises a solid solution in a polyoxyalkylene matrix of apara-di-substituted benzene derivative represented by the formula:##STR2## wherein A denotes an electron donative group and B denotes anelectron attractive group.

According to another aspect of the present invention, there is alsoprovided a method for orientation of a nonlinear optical material, whichcomprises heating the above mentioned nonlinear optical material to orabove the melting temperature, and cooling the material to below themelting point while applying a direct electric field thereto.

These and other objects, features and advantages of the presentinvention will become more apparent upon a consideration of thefollowing description of the preferred embodiments of the presentinvention taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of an example of an opticalmodulation system including a nonlinear optical element composed of anonlinear optical material according to the present invention;

FIG. 2 is a phase diagram of a composition used in Example 8 appearinghereinafter;

FIG. 3 is a graph showing the dependence of the nonlinear optical effectof a nonlinear optical material system on the compositional change ofthe system; and

FIG. 4 is a graph showing the dependence of a nonlinear optical effectof a nonlinear optical material on applied voltage.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The polyoxyalkylene used in the present invention comprises oxyalkyleneunits represents by the formula: ##STR3## wherein R denotes an alkylenegroup containing 1-6 carbon atoms (i.e., C₁ -C₆ alkylene group), and nis 2 or more, preferably 10-200,000, representing the total number ofthe oxyalkylene units in the polyoxyalkylene. The number of the alkyleneunits in the polyoxyalkylene can vary widely as described above as faras the polyoxyalkylene is provided with a film-formability and containsat least two successive oxyalkylene units.

If the alkylene group R contains more than 6 carbon atoms, thepolyoxyalkylene is caused to have a poor mutual solubility with theorganic guest compound having an electron donative group or/and anelectron attractive group, thus failing to provide a film with excellentproperties. It is especially preferred that the alkylene group Rcontains 2-4 carbon atoms.

The polyoxyalkylene constituting the matrix of the nonlinear opticalmaterial according to the present invention may be a homopolymerconsisting of the units represented by the formula (1) alone but canalso be a copolymer or a derivative containing the unit of the formula(1) as a partial structure including two or more, preferably 10 or more,successive polyoxyalkylene units in a proportion of 10 mol % or more,preferably 30 mol % or more in the polyoxyalkylene. Such a copolymer mayassume various forms as follows.

1. A copolymer containing the unit of the formula (1) in its side chainrepresented by the following structure: ##STR4## wherein m is 10 ormore, and n1 is 2 or more. The unit .paren open-st.R--O.parenclose-st._(n1) can be connected to at least a part of the main chainrepresented by .paren open-st.A.paren close-st._(m) and can also form acrosslinking structure.

2. A block polymer containing various forms of the unit (1) in its mainchain as represented by the formula: ##STR5##

3. A copolymer assuming a cyclic structure as a combination of 1. and/or2 as described above.

In the above, the units A, B and C may for example be one selected fromthe following:

recurring units derived from olefin derivatives, such as: ##STR6##recurring units derived from diolefin derivatives, such as ##STR7##recurring units derived from diolefin derivatives, such as ##STR8##recurring units derived from ester derivatives, such as ##STR9##recurring units derived from azomethine derivatives such as ##STR10##recurring units derived from imide derivatives amide derivatives, suchas ##STR11##

Specific examples of the polyoxyalkylene containing the unit (1) as apartial structure include those represented by the following formulas:##STR12## wherein R is a C₁ -C₆ alkylene group, R₁ and R₂ are each a C₁-C₂₀ alkyl group, and n1 is 2 to 100,000; ##STR13## wherein R is a C₁-C₆ alkylene group, R₃ and R₄ are each H or a C₁ -C₂₀ alkyl group, andn1 and n2 are each 2 to 10,000; ##STR14## wherein R₁, R₂ and R₃ are eacha C₁ -C₆ alkylene group, and n1, n2 and n3 are each 2 to 100,000;##STR15## wherein R is a C₁ -C₆ alkylene group, X is --H, --CH₃ or ahalogen radical, n1 is 10 to 20,000, and m is 10 to 100,000; ##STR16##wherein R is a C₁ -C₆ alkylene group, R₁ is a C₁ -C₁₈ alkylene,cyclohexylene, phenylene, biphenylene or tolylene group, n1 is 10 to100,000 and m is 10 to 10,000; ##STR17## wherein R is a C₁ -C₆ alkylenegroup, R₁ is a C₁ -C₁₈ alkylene, cyclohexylene, phenylene, biphenylene,terphenylene or tolylene group, n1 is 10 to 100,00, and m is 10 to10,000.

The polyoxyalkylene matrix of the present invention may be composed ofthe above-described polyoxyalkylene alone but can be a mixture withanother material, such as polymers inclusive of poly(methylmethacrylate), poly(vinyl acetate), polystyrene, poly(vinylidenefluoride), poly(vinylidene cyanide-vinyl acetate), poly (vinylidenefluoride-tetraluoroethylene), poly(vinylidene cyanide-vinyl propionate),poly(vinylidene cyanide-vinyl benzoate), poly(vinyl alcohol), polyimide,etc., polymer liquid crystals, liquid crystals, and powder of inorganiccompound. In such a case, it is preferred that the polyoxyalkyleneconstitutes more than 10 wt. %, particularly more than 30 wt. %, of theresultant mixture constituting the matrix.

The guest compound or dopant used in the nonlinear optical materialaccording to the present invention may preferably be in the form ofaromatic compounds, such as mono-substituted benzene derivative,di-substituted benzene derivative, tri-substituted benzene derivative,tetra-substituted benzene derivative, mono-substituted biphenylderivative, di-substituted biphenyl derivative, tri-substituted biphenylderivative, tetra-substituted biphenyl derivative, mono-substitutednaphthalene derivative, di-substituted naphthalene derivative,tri-substituted naphthalene derivative, tetra-substituted naphthalenederivative, mono-substituted pyridine derivative, di-substitutedpyridine derivative, tri-substituted pyridine derivative,tetra-substituted pyridine derivative, mono-substituted pyrazinederivative, di-substituted pyrazine derivative, tri-substituted pyrazinederivative, tetra-substituted pyrazine derivative, mono-substitutedpyrimidine derivative, di-substituted pyrimidine derivative,tri-substituted pyrimidine derivative, tetra-substituted pyrimidinederivative, mono-substituted azulene derivative, di-substituted azulenederivative, tri-substituted azulene derivative, tetra-substitutedazulene derivative, mono-substituted pyrrole derivative, di-substitutedpyrrole derivative, tri-substituted pyrrole derivative,tetra-substituted pyrrole derivative, mono-substituted thiophenederivative, di-substituted thiophene derivative, tri-substitutedthiophene derivative, tetra-substituted thiophene derivative,mono-substituted furan derivative, di-substituted furan derivative,tri-substituted furan derivative, tetra-substituted furan derivative,mono-substituted pyrylium salt derivative, di-substituted pyrylium saltderivative, tri-substituted pyrylium salt derivative, tetra-subsitutedpyrylium salt derivative, mono-substituted quinoline derivative,di-substituted quinoline derivative, tri-substituted quinonelinederivative, tetra-substituted quinoline derivative, mono-substitutedpyridazine derivative, di-substituted pyridazine derivative,tri-substituted pyridazine derivative, tetra-substituted pyridazinederivative, mono-substituted triazine derivative, di-substitutedtriazine derivative, tri-substituted triazine derivative,mono-substituted tetrazine derivative, di-substituted tetrazinederivative, mono-substituted anthracene derivative, di-substitutedanthracene derivative, tri-substituted anthracene derivative, ortetra-substituted anthracene derivative.

Examples of the electron donative group attached to the guest compoundas described above may include: amino group, alkyl group (methyl, ethyl,isopropyl, n-propyl, n-butyl, t-butyl, sec-butyl, n-octyl, t-octyl,n-hexyl, cyclohexyl, etc.), alkoxy group (methoxy, ethoxy, propoxy,butoxy, etc.), alkylamino group (N-methylamino, N-ethylamino,N-propylamino, N-butylamino, etc.), hydroxyalkylamino group(N-hydroxymethylamino, N-(2-hydroxyethyl)amino,N-(2-hydroxypropyl)amino, N-(3-hydroxypropyl)amino,N-(4-hydroxybutyl)amino, etc.), dialkylamino group (N,N-dimethylamino,N,N-diethylamino, N,N-dipropylamino, N,N-dibutylamino,N-methyl-N-ethylamino, N-methyl-N-propylamino, etc.),hydroxyalkyl-alkylamino group (N-hydroxymethyl-N-methylamino,N-hydroxymethyl-N-ethylamino, N-hydroxymethyl-N-ethylamino,N-(2-hydroxyethyl)-N-methylamino, N-(2-hydroxyethyl)-N-ethylamino,N-(3-hydroxypropyl)-N-methylamino, N-(2-hydroxypropyl)-N-ethylamino,N-(4-hydroxybutyl)-N-butylamino, etc.), dihydroxyalkylamino group(N,N-dihydroxymethylamino, N,N-di-(2-hydroxyethyl)amino,N,N-di-(2-hydroxypropyl)amino, N,N-di-(3-hydroxypropyl)amino,N-hydroxymethyl-N-(2-hydroxyethyl)amino, etc.), mercapto group andhydroxy group.

On the other hand, examples of the electron attractive group mayinclude: nitro group, cyano group, haloge atom (fluorine, chlorine,bromine), trifluoromethyl group, carboxyl group, carboxy ester group,carbonyl group and sulfonyl group.

Specific examples of the guest compound which may be used in the presentinvention may include the following:

(1) 3-nitro-4-hydroxy-3-sodiumcarboxy-azobenzene,

(2) 4-chloro-2-phenylquinazoline,

(3) aminoadipic acid,

(4) aminoanthracene,

(5) aminobiphenyl,

(6) 2-amino-5-bromobenzoic acid,

(7) 1-amino-5-bromobenzoic acid,

(8) 1-amino-4-bromonaphthalene,

(9) 2-amino-5-bromopyridine,

(10) amino-chlorobenzenesutfonic acid,

(11) 2-amino-4-chlorobenzoic acid,

(12) 2-amino-5-chlorobenzoic acid,

(13) 3-amino-4-chlorobenzoic acid,

(14) 4-amino-2-chlorobenzoic acid,

(15) 5-amino-2-chlorobenzoic acid,

(16) 2-amino-5-chlorobenzonitrile,

(17) 2-amino-5-chlorobenzophenone,

(18) amino-chlorobenzotrifluoride,

(19) 3-amino-6-chloromethyl-2-pyrazinecarbonitrile-4oxide,

(20) 2-amino-4-chloro-6-methylpyridine,

(21) 1-amino-4-chloronaphthalene,

(22) 2-amino-3-chloro-1,4-naphthoquinone,

(23) 2-amino-4-chloro-5-nitrophenol,

(24) 2-amino-4-chloro-5-nitrotoluene,

(25) 2-amino-4-chloro-4-phenol,

(26) 2-amino-5-chloropurine,

(27) 2-amino-5-chloropyridine,

(28) 3-amino-2-chloropyridine,

(29) 5-amino-2-chloropyridine,

(30) aminochrysene,

(31) 2-amino-p-cresol,

(32) 3-amino-p-cresol,

(33) 4-amino-p-cresol,

(34) 4-amino-m-cresol,

(35) 6-amino-m-cresol,

(36) 3-aminocrotononitrile,

(37) 6-amino-3-cyano-2,4-dimethylpyridine,

(38) 5-amino-6-cyano-2-pyrazinyl acetate,

(39) 4-[N-(2-methyl-3-cyano-5-pyrazinylmethyl)amino]-benzoic acid,

(40) 3,5-dinitroaniline,

(41) 4-(2,4-dinitroanilino)phenol,

(42) 2,4-dinitroanisol,

(43) 2,4-dinitrobenzaldehyde,

(44) 2,6-dinitrobenzaldehyde,

(45) 3,5-dinitrobenzamide,

(46) 1,2-dinitrobenzene,

(47) 1,3-dinitrobenzene,

(48) 3,4-dinitrobenzoic acid,

(49) 3,5-dinitrobenzoic acid,

(50) 3,5-dinitrobenzonitrile,

(51) 2,6-dinitro-p-cresol,

(52) 4,6-dinitro-o-cresol,

(53) 2,4-dinitrodiphenylamine,

(54) dinitrodurene,

(55) 2,4-dinitro-N-ethylaniline,

(56) 2,7-dinitrofluorenone,

(57) 2,4-dinitrofluorobenzene,

(58) 1,3-dinitronaphthalene,

(59) 1,5-dinitronaphthalene,

(60) 1,8-dinitronaphthalene,

(61) 2,4-dinttrophenol,

(62) 2,5-dinitrophenol,

(63) 2,4-dinitrophenylhydrazine,

(64) 3,5-dinitrosalicylic acid,

(65) 2,3-dinitrotoluene,

(66) 2,4-dinitrotoluene,

(67) 2,6-dinitrotoluene,

(68) 3,4-dinitrotoluene,

(69) 9-nitroanthracene,

(70) 4-nitroanthranilic acid,

(71) 2-amino-5-trifluoromethyl-1,3,4-thiazole,

(72) 7-amino-4-(trifluoromethyl)-coumarine,

(73) 9-cyanoanthracene,

(74) 3-cyano-4,6-dimethyl-2-hydroxypyridine,

(75) 5-cyanoindole,

(76) 2-cyano-6-methoxybenzothiazole,

(77) 9-cyanophenanthrene,

(78) cyanuric chloride,

(79) 1,2-diaminoanthraquinone,

(80) 3,4-diaminobenzoic acid,

(81) 3,5-diaminobenzoic acid,

(82) 3,4-diaminobenzophenone,

(83) 2,4-diamino-6-(hydroxymethy)pteridine,

(84) 2,6-diamino-4-nitrotoluene,

(85) 2,3-dicyanohydroquinone,

(86) 2,6-dinitroaniline,

(87) 2-amino-5-iodobenzoic acid,

(88) aminomethoxybenzoic acid,

(89) 2-amino-4-methoxybenzothiazole,

(90) 2-amino-6-methoxybenzothiazole,

(91) 5-amino-2-metoxyphenol,

(92) 5-amino-2-methoxypyridine,

(93) 2-amino-3-methylbenzoic acid,

(94) 2-amino-5-methylbenzoic acid,

(95) 2-amino-6-methylbenzoic acid,

(96) 3-amino-4-methylbenzoic acid,

(97) 4-amino-3-methylbenzoic acid,

(98) 2-amino-4-methylbenzophenone,

(99) 7-amino-4-methylcoumarin,

(100) 3-amino-5-methylisoxazole,

(101) 7-amino-4-methy-1,8-naphthylidene-2-ol.

As described hereinbefore, a preferred class of the guest compounds arethose of a para-di-substituted benzene structure, particularly thoserepresented by the formula (1) above having both an electron donativegroup and an electron attractive group. Examples thereof may include thefollowing:

(111) 4-aminoacetophenone,

(112) 4-aminobenzoic acid,

(113) 4-amino-α,α,α-trifluorotoluene,

(114) 4-amino-benzonitrile,

(115) 4-aminocinnamic acid,

(116) 4-aminophenol,

(117) 4-bromotoluene,

(118) 4-bromoaniline,

(119) 4-bromoanisole,

(120) 4-bromobenzaldehyde,

(121) 4-bromobenzonitrile,

(122) 4-chlorotoluene,

(123) 4-chloroaniline,

(124) 4-chloroanisole,

(125) 4-chlorobenzaldehyde,

(126) 4-chlorobenzonitrile,

(127) 4-chanobenzaldehyde,

(128) α-cyano-4-hydroxycinnamic acid,

(129) 4-cyanophenol,

(130) 4-cyanopyridine-N-oxide,

(131) 4-fluorotoluene,

(132) 4-fluoroaniline,

(133) 4-fluoroanisole,

(134) 4-fluorobenzaldehyde,

(135) 4-fluorobenzonitrile,

(136) 4-nitroaniline,

(137) 4-nitrobenzamide,

(138) 4-nitrobenzojc acid,

(139) 4-nitrobenzyl alcohol,

(140) 4-nitrocinnamaldehyde,

(141) 4-nitrocinnamic acid,

(142) 4-nitrophenol,

(143) 4-nitrophenetole,

(144) 4-nitrophenyl acetate,

(145) 4-nitrophenylhydrazine,

(146) 4-nitrophenyl isocyanate

(147) 4-nitrotoluene

(148) 4-nitro-α,α,α-trifluorotoluene.

The guest compound as described above may be contained in the nonlinearoptical material according to the present invention in a proportion of5-80 wt. parts, preferably 10-70 wt. parts, per 100 wt. parts of thepolyoxyalkylene matrix. Too little guest compound is not desirablebecause of a small nonlinear susceptibility. On the other hand, too muchguest compound is not desirable because the resultant nonlinear opticalmaterial loses a polymer characteristic.

The para-di-substituted benzene derivative represented by the formula(1) has a large intra-molecular dipole moment because it has an electrondonative group and an electron attractive group at its para positions.On the other hand, the second order micro-nonlinear optical constant orpolarization of a molecule is represented by the following formula:##EQU1## wherein ω .sub.(ng) denotes an energy difference between theground and excited state; h, the Planch's constant, ri.sub.(gn), adipole matrix element between the ground and excited states; e, a unitelectron charge; and Δri.sub.(n) =ri.sub.(nn) -ri.sub.(gg) (Ward, J. F.;Review of Modern Physics, Vol. 37, page 1 (1965)). As is understood fromthe above equation, a benzene derivative having polar substituents atits para-positions and having a large dipole moment provides a largesecond-order nonlinear constant β. However, a compound having a largedipole moment, such as a para-di-substituted benzene derivative, isliable to have an inversion symmetrical center and does not cause SHG inmost cases.

It contrast thereto, in the nonlinear optical material according to thepresent invention, it has become possible to cause such apara-di-substituted benzene derivative to show an SHG activity by addingit as a guest in the polyoxyalkylene matrix. In other words, in thepresent invention, it has become possible to remove the inversionsymmetrical center or centrosymmetry of such a compound having a largedipole moment by the presence of the polyoxyalkylene matrix. It isconsidered that the removal of the centrosymmetry may be caused becausethe polyoxyalkylene forms helixes in its crystalline state and theabove-mentioned guest compound is uniaxially orientd on aligned betweenthe helixes.

Because the quest compound interacts with the helical structure of thepolyoxyalkylene matrix to be uniaxially oriented, phase separation orununiform crystallization is not caused even if the guest compounds iscontained in a large proportion. Similarly, because the helicalstructure of the polyoxyalkylene matrix is retained, the nonlinearoptical material according to the present invention retains goodflexibility and mechanical strength and is suitably used in the form ofa film or fiber.

Further, because the polyoxyalkylene matrix and the guest compound arealigned in a unique manner through the interaction therebetween in thenonlinear optical material of the invention, the nonlinear opticalmaterial can assume a high degree of orientation through an orientationtreatment under the action of electric field, magnetic field,stretching, etc., to an extent which cannot be realized in principlebased on the above-mentioned reports by Meredity, G. R. et al andSinger, K. D., et al.

As such an orientation treatment, it is desirable to heat the nonlinearoptical material to a temperature above the melting point where thepolyoxyalkylene matrix and the quest compound do not interact with eachother, and cool the mixture to below the melting point while applying anelectric field in a direction equal to the photoelectric field ofincident light for causing a nonlinear optical effect. At this time, anexcellent nonlinear optical effect is attained by cooling the materialat a rate of 100° C./sec or below, preferably 10° C./sec or below, so asto maximize the interaction between the polyoxyalkylene matrix and theguest compound under the action of the electric field.

FIGS. 3 and 4 show patterns of changes in SHG intensity of a nonlinearoptical material system oriented under an electric field dependent onthe content of a guest compound at a constant electric field (FIG. 3)and depending on the electric field intensity at a certain composition(FIG. 4), respectively.

When the nonlinear optical material according to the present inventionis subjected to an orientation treatment as described above, the dipolemoments of the guest compound molecules therein are uniformly aligned inthe electric field direction so as to provide the largestmicro-nonlinear optical constant β in a direction perpendicular to thefilm surface. As a result, the nonlinear optical effect as a filmwaveguide can be utilized to the maximum.

Similar orientation or molecular alignment effect can be obtained byheating the nonlinear optical material to above the melting point,followed by cooling under the application of a magnetic field. Thenonlinear optical material can also be stretched for effectiveorientation.

The nonlinear optical material according to the present invention mayfor example be formed into a nonlinear optical element in the form of,e.g., a film having a thickness of, e.g., 0.01 to 100 mm, by adding theguest compound having an electron donative group and/or a electronattractive group into a solution of the polyoxyalkylene in anappropriate solvent, such as benzene, acetonitrile and lower alcohols toprepare a uniform solution and forming the solution into a film as bycasting, spin coating, dipping, etc., followed by drying. At this time,it is preferable to effect heating at a temperature of 40°-120° C. inorder to provide a good film with good compatibility between thepolyoxyalkylene matrix and the guest compound. As described above, it ispreferable to apply a DC electric field of, e.g., 50 V/cm-10⁶ V/cm,preferably 100 V/cm-10⁵ V/cm to the film above the melting point andcool the film under the electric field. The application of the DCelectric field may be effected, e.g., by providing electrodes on bothsides of the film or by corona discharging.

In the nonlinear optical material thus formed according to the presentinvention either before or after the orientation treatment, the guestcompound is present in the form of a solid solution in thepolyoxyalkylene matrix. The fact that the guest compound is in its solidsolution state, i.e., free from crystallization, may for example beconfirmed by the absence of an X ray diffraction peak attributable tothe crystal of the guest compound when a sample nonlinear opticalmaterial, of e.g., a 0.1 to 2 mm-thick film, is subjected to thereflection X-ray analysis by means of an X-ray diffractometer (e.g.,Model RAD-III, available from Rigaku Denki K. K.) or by the absence of aheat-absorption peak or shoulder attributable to the crystal of theguest compound when a sample is subjected to heating at a temperature ata rate of 5°-10° C./min by means of a DSC (differential scanningcalorimeter).

FIG. 1 schematically illustrates an example of an optical modulationsystem incorporating a nonlinear optical material 1 shown in the form ofa section comprising therein a waveguide 14 formed of a nonlinearoptical material according to the present invention. Referring to FIG.1, the nonlinear optical material 1 comprises a substrate 11 of, e.g.glass, plastic, etc.; a lower electrode 12 formed of a conductor, suchas ITO (indium-tin-oxide), tin oxide, indium oxide, gold, silver, copperor aluminum; a low-reflective index layer 14 in the form of a film of anorganic material such as vinylidene fluoride-trifluoroethylene copolymeror an inorganic material such as SiO₂ ; the waveguide 14 of a nonlinearoptical material according to the present invention in a thickness of,e.g., 0.1 to 10 microns, preferably 0.3 to 3 microns, and an upperelectrode 15 of, e.g., aluminum.

In operation, a laser beam having a wavelength of λ₀ emitted from alaser source 16 after passing through an optical modulator 17 such as anoptical switching element or an optical deflector and a condenser lens18 is incident on the nonlinear optical material 1 to be converted intoa second harmonic having a wavelength λ₀ /2 for output.

Hereinbelow, the present invention is explained based on Examples.

EXAMPLE 1

A glass substrate coated with a vapor-deposited aluminum film wasfurther spin-coated with a solution obtained by dissolving 2.03 g (40mmol) of polyoxyethylene with a molecular weight of 5×10⁶ and 0.38 g (2mmol) of 1-amino-4-nitronaphthalene in 5 ml of benzene for 5 hours,followed by drying at 60°-80° C. to obtain an about 1 micron-thickuniform film. Further, an aluminum electrode was formed thereon bysputtering to obtain a waveguide-type nonlinear optical element. Theelement was heated at 80° C. and then cooled to room temperature underthe application of an electric field of 100 V between the aluminumelectrodes on both ides. The nonlinear optical element was irradiatedwith an Nd-YAG laser beam (wavelength (λ)=1.064 microns) after focusing,whereby the generation of a second harmonic (wavelength (λ)=0.532micron) was observed through a photomultiplier.

EXAMPLE 2

A glass substrate coated with a vapor-deposited aluminum film wasfurther spin-coated with a 5 wt. % solution of vinylidenefluoride-tetrafluoro-ethylene copolymer in MEK, followed by drying toform a film thereon. The glass substrate was further spin-coated with asolution obtained by dissolving 1.03 g (23 mmol) of polyoxyethylene witha molecular weight of 5×10⁶ and 0.20 g (1 mmol) of2,4-dinitrophenyl-hydrazine in 10 ml of acetonitrile, followed by dryingat 60°-80° C. to obtain an about 1 micron-thick uniform film. Further,an aluminum electrode was formed thereon by sputtering to obtain awaveguide-type nonlinear optical element. The element was heated at 80°C. and then cooled to room temperature under the application of anelectric field of 200 V between the aluminum electrodes on both sides.The nonlinear optical element was irradiated with an Nd-YAG laser beam(wavelength (λ)=1.064 microns) after focusing, whereby the generation ofa second harmonic wavelength (λ)=0.532 micron) was observed through aphotomultiplier.

EXAMPLE 3

1.0 g of polyethylene qlycol distearate (RCOO(CH₂ CH₂ O)_(n) COOR, R=C₁₇H₃₅, averaqe molecular weight (Mw of about 1500): "Emanon 3299"available from Kao K. K.) and 0.2 g of 4-nitro-4'-iodobiphenyl wereadded to 3 ml of methanol and the mixture was dissolved under heatingfor 1 hour. The resultant solution was cast onto a petri dish to beformed into an about 200 micron-thick uniform film.

An aluminum foil was applied onto both sides of the film, and thelaminate was heated to 80° C. and then gradually cooled to roomtemperature while applying a DC electric field of 1000 V. The electrodeswere removed from the film, and the film was irradiated with an Nd-YAGlaser (λ=1.064 microns), whereby an optical second harmonic (λ=0.532micron) was observed in scattered light through a photomultiplier at anintensity about 3 times that obtained with urea according to the powdermethod.

EXAMPLE 4

1.0 g of a polyethylene glycol derivative (Mw=about 345; "DA-350F"available from Nihon Yushi K. K.) represented by the formula: ##STR18##and 0.2 g of 4-methoxy-4"'-cyanoterphenyl were added to 20 ml of ethanoland the mixture was dissolved under heating for 1 hour. The resultantsolution was cast onto a petri dish to be formed into an about 200micron-thick uniform film.

An aluminum foil was applied onto both sides of the film, and thelaminate was heated to 80° C. and then gradually cooled to roomtemperature while applying a DC electric field of 1000 V. The electrodeswere removed from the film, and the film was irradiated with an Nd-YAGlaser (λ=1.064 microns), whereby an optical second harmonic (λ=0.532micron) was observed in scattered light through a photomultiplier at anintensity about 4 times that obtained with urea according to the powdermethod.

EXAMPLE 5

1.0 g of an ethylene oxide-propylene oxide block copolymer (Mw=3250;"PE-68" available from Sanyo Kasei K. K.) represented by the formula:##STR19## and 0.2 g of 2-(4'-amino)-5,6-dicyano-1,4-pyradine weredissolved in a solvent mixture of 20 ml of benzene and 10 ml of methanolunder heating. The resultant solution was cast onto a petri dish to beformed into an about 100 micron-thick uniform film.

An aluminum foil was applied onto both sides of the film, and thelaminate was heated to 80° C. and then gradually cooled to roomtemperature while applying a DC electric field of 1000 V. The electrodeswere removed from the film, and the film was irradiated with an Nd-YAGlaser (λ=1.064 microns), whereby an optical second harmonic (λ=0.532micron) was observed in scattered light through a photomultiplier at anintensity about 2 times that obtained with urea according to the powdermethod.

EXAMPLE 6

1.0 g of polyoxyethylene (Mw=5×10⁶), 0.25 g of butyral resin ("BL-1"available from Sekisui Kagaku K. K.) and 0.25 g of1-amino-4-nitronaphthalene were dissolved in a solvent mixture of 20 mlof benzene and 10 ml of methanol under heating. The resultant solutionwas cast onto a petri dish to be formed into an about 200 micron-thickuniform film.

An aluminum foil was applied onto both sides of the film, and thelaminate was heated to 80° C. and then gradually cooled to roomtemperature while applying a DC electric field of 1000 V. The electrodeswere removed from the film, and the film was irradiated with an Nd-YAGlaser (λ=1.064 microns), whereby an optical second harmonic (λ=0.532micron) was observed in scattered light through a photomultiplier at anintensity about 3 times that obtained with urea according to the powdermethod.

EXAMPLE 7

1.03 g (23 mmol) of polyoxyethylene (POE) (Mw=2×10⁴) and 0.44 g (3 mmol)of para-nitroaniline (P-NA) were added to 10 ml of benzene and dissolvedunder heating for 5 hours. The solution was charged onto a petri dishand dried at 60°-80° C. to obtain a uniform film.

The film was irradiated with an Nd-YAG laser (λ=1.064 microns), wherebyan optical second harmonic (λ=0.532 micron) was observed through aphoto-multiplier at an intensity of about 5% of that obtained with ureaaccording to the powder method.

EXAMPLE 8

Polyoxyethylene (POE) (Mw=6×10⁵) and para-nitroaniline (P-NA) in variousproportions were dissolved in acetonitril under heating in a similarmanner as in Example 7 and the resultant solutions were respectivelydried on a petri dish to form several compositions in the form of films.

The compositions were subjected to measurement of phase transitiontemperatures by means of a differential scanning calorimeter ("DSC-7"available from Perkin Elmer Inc.). FIG. 2 shows a phase diagram of thissystem based on the results of the abov measurement.

EXAMPLE 9

2.12 g (48 mmol) of polyoxyethylene (Mw=5×10⁶) and 1.57 g (11 mmol) ofpara-nitroaniline were dissolved in 100 ml of acetonitril under heatingfor 5 hours. The solution was cast on a petri dish and dried at 60°-80°C. to form a 200 micron-thick uniform film.

An aluminum foil was applied on both sides of the film, and the laminatewas heated to 80° C. under application of a DC electric field of 1000 Vand then gradually cooled to room temperature. After removing theelectrodes, the film was irradiated with an Nd-YAG film (λ=1.064microns), whereby an optical second harmonic (λ=0.532 microns) wasobserved through a photomultiplier at an intensity of about 8 times thatobtained with urea according to the powder method.

EXAMPLE 10

1.0 g of polyethylene glycol distearate (RCOO(CH₂ CH₂ O)_(n) COOR, R=C₁₇H₃₅, average molecular weight (Mw): "Emanon 3299" available from Kao K.K.) and 0.2 g of para-nitroaniline were added to 30 ml of methanol andthe mixture was dissolved under heating for 1 hour. The resultantsolution was cast onto a petri dish to be formed into an about 200micron-thick uniform film.

An aluminum foil was applied onto both sides Rof the film, and thelaminate was heated to 80° C. and then gradually cooled to roomtemperature while applying a DC electric field of 1000 V. The electrodeswere removed from the film, and the film was irradiated with an Nd-YAGlaser (λ=1.064 microns), whereby an optical second harmonic (λ=0.532micron) was observed in scattered light through a photomultiplier at anintensity about 6 times that obtained with urea according to the powdermethod.

EXAMPLE 11

1.0 g of a polyethylene glycol derivative (Mw=about 345; "DA-350F"available from Nihon Yushi K. K.) representd by the formula: ##STR20##and 0.2 g of p-nitroaniline were added to 20 ml of ethanol and themixture was dissolved under heating for 1 hour. The resultant solutionwas cast onto a petri dish to form an about 200 micron-thick uniformfilm.

An aluminum foil was applied onto both sides of the film, and thelaminate was heated to 80° C. and then gradually cooled to roomtemperature while applying a DC electric field of 1000 V. The electrodeswere removed from the film, and the film was irradiated with an Nd-YAGlaser (λ=1.064 microns), whereby an optical second harmonic (λ=0.532micron) was observed in scattered light through a photomultiplier at anintensity about 8 times that obtained with urea according to the powdermethod.

EXAMPLE 12

1.0 g of an ethylene oxide-propylene oxide block copolymer (Mw=3250;"PE-68" available from Sanyo Kasei K. K.) represented by the formula:##STR21## and 0.2 g of p-nitroaniline were dissolved in a solventmixture of 20 ml of benzene and 10 ml of methanol under heating. Theresultant solution was cast onto a petri dish to form into an about 200micron-thick uniform film.

An aluminum foil was applied onto both sides of the film, and thelaminate was heated to 80° C. and then gradually cooled to roomtemperature while applying a DC electric field of 1000 V. The electrodeswere removed from the film, and the film was irradiated with an Nd-YAGlaser (λ=1.064 microns), whereby an optical second harmonic (λ=0.532micron) was observed in scattered light through a photomultiplier at anintensity about 8 times that obtained with urea according to the powdermethod.

EXAMPLE 13

1.0 g of polyoxyethylene (Mw=5×10⁶), 0.25 g of butyral resin ("BL-1"available from Sekisui Kagaku K. K.) and 0.25 g of p-nitroaniline weredissolved in a solvent mixture of 20 ml of benzene and 10 ml of methanolunder heating. The resultant solution was cast onto a petri dish to forminto an about 200 micron-thick uniform film.

An aluminum foil was applied onto both sides of the film, and thelaminate was heated to 80° C. and then gradually cooled to roomtemperature while applying a DC electric field of 1000 V. The electrodeswere removed from the film, and the film was irradiated with an Nd-YAGlaser (λ=1.064 microns), whereby an optical second harmonic (λ=0.532micron) was observed in scattered light through a photomultiplier at anintensity about 15 times that obtained with urea according to the powdermethod.

EXAMPLE 14

1.0 g of polyoxytetramethylene glycol (Mw=3000; "PTMG 3000" availablefrom Sanyo Kasei K. K.) and 0.2 g of para-nitroaniline were dissolvedunder heating in a mixture solvent of 30 ml of benzene and 10 ml ofmethanol. The resultant solution was cast onto a petri dish to form anabout 200 micron-thick uniform film

An aluminum foil was applied onto both sides of the film, and thelaminate was heated to 80° C. and then gradually cooled to roomtemperature while applying a DC electric field of 1000 V. The electrodeswere removed from the film, and the film was irradiated with an Nd-YAGlaser (λ=1.064 microns), whereby an optical second harmonic (λ=0.532micron) was observed in scattered light through a photomultiplier at anintensity about 10 times that obtained with urea according to the powdermethod.

As described above, the nonlinear optical material according to thepresent invetion can be very easily formed into a waveguide in the formof a film or fiber. By using a nonlinear optical element thus formed ina simple structure, a large nonlinear optical effect can be obtained.Based on these effects, the nonlinear optical material according to thepresent invention can be formed into a nonlinear optical element whichis applicable to an optical integrated circuit or an opto-electronicintegrated circuit.

Further, according to the present invention, it has become possible toconvert a polyoxyalkylene and a para-di-substituted benzene derivativenot showing a nonlinear optical effect into a nonlinear optical materialshowing a large nonlinear optical effect (SHG) which is expected from aninherently or potentially large micro nonlinear optical constant. Thethus composed nonlinear optical material can be formed into a filmhaving excellent mechanical and optical properties, so that it isreadily applicable to an optical integrated circuit and anopto-electronic circuit.

What is claimed is:
 1. An optical modulation system comprising:a laser,and an optical modulator including a film of a nonlinear opticalmaterial and an electrode disposed on said film, said nonlinear opticalmaterial, comprising: a solid solution of from 5-80 parts by weight of acentrosymmetric para-disubstituted organic guest compound showing nosecond harmonic generation (SHG) by itself and having a molecular dipolemoment in 100 parts by weight of polyoxyalkylene matrix, wherein thepolyoxyalkylene matrix comprises oxyalkylene units of the formula (1)below at least as a partial structure including two or more successiveoxyalkylene units in a proportion of 30 mol % or more in thepolyoxyalkylene, Formula (1): (R--O)_(n),wherein R denotes an alkylenegroup containing 1-6 carbon atoms, and n is 2-200,000; and the organicguest compound comprises a para-disubstituted benzene ring to which anelectron donative group and an electron attractive group are attached toprovide the molecular dipole moment, wherein said electron donativegroup is an amino group, alkyl group, alkoxy group, alkylamino group,hydroxyalkylamino group, dialkylamino group, hydroxyalkyl-alkylaminogroup, dihydroxyalkylamino group, mercapto group, or hydroxy group; andsaid electron attractive group is a nitro group, cyano group, halogenatom, trifluoromethyl group, carboxyl group, carboxy ester group,carbonyl group or sulfonyl group.
 2. An optical modulation systemaccording to claim 1, wherein said polyoxyalkylene is represented by theformula: ##STR22## wherein R₁ and R₂ each denote an alkyl group having1-20 carbon atoms, and n1 is 2-100,000.
 3. An optical modulation systemaccording to claim 1, wherein said polyoxyalkylene is represented by theformula: ##STR23## wherein R₃ and R₄ each denote hydrogen or an alkylgroup having 1-20 carbon atoms and n1 and n2 are each 2 to 100,000. 4.An optical modulation system according to claim 1, wherein saidpolyoxyalkylene is represented by the formula: ##STR24## wherein R₁, R₂and R₃ each denote an alkylene group having 1-6 carbon atoms and n1, n2and n3 are each 2-100,000.
 5. An optical modulation system according toclaim 1, wherein said polyoxyalkylene is represented by the formula:##STR25## wherein X denotes H--, CH₃ -- or a halogen atom, and m is10-100,000.
 6. An optical modulation system according to claim 1,wherein said polyoxyalkylene is represented by the formula: ##STR26##wherein n1 is 10-100,000, R₁ denotes an alkylene group having 1-18carbon atoms, cyclohexylene group, phenylene group, biphenylene group,or tolylene group, and m is 10-10,000.
 7. An optical modulation systemaccording to claim 1, wherein said polyoxyalkylene is represented by theformula: ##STR27## wherein n1 is 10-100,000, R₁ is an alkylene grouphaving 1-18 carbon atoms, cyclohexylene group, phenylene group,biphenylene group, terphenylene group or tolyene group, and m is10-10,000.
 8. An optical modulation system according to claim 1, whereinsaid guest compound is a para-di-substituted benzene derivativerepresented by the formula: ##STR28## wherein A is the electron donativegroup and B is the electron attractive group.
 9. An optical modulationsystem according to claim 1 wherein said solid solution is oriented sothat the molecular dipole moment of the organic guest compound in apolyoxyalkylene matrix is aligned in one direction.
 10. An opticalmodulation system according to claim 9, wherein said polyoxyalkylene isrepresented by the formula:

    R.sub.1 COO(R--O).sub.n1 COOR.sub.2,

wherein R₁ and R₂ each denote an alkyl group having 1-20 carbon atoms,and n1 is 2-100,000.
 11. An optical modulation system according to claim9, wherein said polyoxyalkylene is represented by the formula: ##STR29##wherein R₃ and R₄ each denote hydrogen or an alkyl group having 1-20carbon atoms and n1 and n2 are each 2 to 100,000.
 12. An opticalmodulation system according to claim 9, wherein said polyoxyalkylene isrepresented by the formula: ##STR30## wherein R₁, R₂ and R₃ each denotean alkylene group having 1-6 carbon atoms and n1, n2 and n3 are each2-100,000.
 13. An optical modulation system according to claim 9,wherein said polyoxyalkylene is represented by the formula: ##STR31##wherein X denotes H--, CH₃ -- or a halogen atom, and m is 10-100,000.14. An optical modulation system according to claim 9, wherein saidpolyoxyalkylene is represented by the formula: ##STR32## wherein n1 is10-100,000, R₁ denotes an alkylene group having 1-18 carbon atoms,cyclohexylene group, phenylene group, biphenylene group, or tolylenegroup, and m is 10-10,000.
 15. An optical modulation system according toclaim 9, wherein said polyoxyalkylene is represented by the formula:##STR33## wherein n1 is 10-1000,000, R₁ is an alkylene group having 1-18carbon atoms, cyclohexylene group, phenylene group, biphenylene group,terphenylene group or tolylene group, and m is 10-10,000.
 16. An opticalmodulation system according to claim 9, wherein said guest compound is apara-di-substituted benzene derivative represented by the formula:##STR34## wherein A is the electron donative group and B is the electronattractive group.